<template>
    <div class="slider" ref="slider">
      <div class="slider-group" ref="sliderGroup">
        <slot></slot>
      </div>
      <div class="dots">
        <span
          class="dot"
          :class="{active: currentPageIndex === index}"
          v-for="(dot, index) in dots"
          :key="index"></span>
      </div>
    </div>
</template>

<script>
import BScroll from 'better-scroll'
import {addClass} from 'common/js/dom'
export default {
  name: 'slider',
  props: {
    loop: {
      type: Boolean,
      default: true
    },
    autoplay: {
      type: Boolean,
      default: true
    },
    interval: {
      type: Number,
      default: 4000
    }
  },
  data () {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  mounted () {
    // 面刷新大概是17毫秒
    setTimeout(() => {
      this._setSliderWidth()
      this._initSlider()
      this._initDots()
      if (this.autoplay) {
        this._play()
      }
    }, 20)
    // 监听页面的视口是否变化，如果发生了变化，做出相应的方法
    window.addEventListener('resize', () => {
      if (!this.slider) {
        return
      }
      this._setSliderWidth(true)
      // sliderGroup发生了变化，刷新this.slider
      this.slider.refresh()
    })
  },
  methods: {
    _setSliderWidth (isResize) {
      this.children = this.$refs.sliderGroup.children
      let width = 0
      let sliderWidth = this.$refs.slider.clientWidth
      for (let i = 0; i < this.children.length; i++) {
        let child = this.children[i]
        addClass(child, 'slider-item')
        child.style.width = sliderWidth + 'px'
        width += sliderWidth
      }
      if (this.loop && !isResize) {
        width += 2 * sliderWidth
      }
      this.$refs.sliderGroup.style.width = width + 'px'
    },
    _initSlider () {
      this.slider = new BScroll(this.$refs.slider, {
        scrollX: true,
        scrollY: false,
        // 当快速在屏幕上滑动一段距离的时候，会根据滑动的距离和时间计算出动量，并生成滚动动画
        momentum: false,
        // 这个配置是为了做 Slide 组件用的
        snap: {
          loop: this.loop,
          threshold: 0.3
        }
      })
      // 监听事件,获取轮播页面的码数
      this.slider.on('scrollEnd', () => {
        let pageIndex = this.slider.getCurrentPage().pageX
        this.currentPageIndex = pageIndex
        // 事件scrollEnd每次被触发时候就调用该函数。
        if (this.autoplay) {
          clearTimeout(this.timer)
          this._play()
        }
      })
    },
    _initDots () {
      this.dots = new Array(this.children.length - 2)
      console.log(this.children.length)
    },
    _play () {
      let pageIndex = this.currentPageIndex + 1
      if (pageIndex >= 5) {
        pageIndex = 0
      }
      this.timer = setTimeout(() => {
        this.slider.goToPage(pageIndex, 0, 400)
      }, this.interval)
    }
  },
  // 好的编程习惯，在关闭该组件的时候，清理掉她的定时器
  destroyed () {
    clearTimeout(this.timer)
  }
}
</script>

<style lang="stylus">
  @import "~common/stylus/variable"
  .slider
    min-height 1px
    .slider-group
      position relative
      overflow hidden
      white-space normal
      .slider-item
        float left
        box-sizing border-box
        overflow hidden
        text-align center
        & > a
          display block
          width 100%
          overflow hidden
          text-decoration none
          & > img
            display block
            width 100%
            height 100%
    .dots
      position absolute
      right 0
      left 0
      bottom 12px
      text-align center
      .dot
        display inline-block
        margin 0 4px
        width 8px
        height 8px
        border-radius 50%
        background $color-text-l
        &.active
          width 20px
          border-radius 5px
          background $color-text-ll
</style>
